Apparatus for intensifying speech in the human vocal cavities



April 17, 1945. D N} R FRENCH 2,374,090 APPARATUS FOR INTENSIFYINGSPEECH IN THE HUMAN VOCAL CAVITIES Filed Dec. 11, 1943v ,8 l7 I0 1 I laNORMAL SPEECH (PLUS REINFORCED SPEECH I EINFORCED SPEECH AMPLITUDEAMBIENT NIOISE n SP EAKER FREQUENCY WV'ENTOR M R FRENCH ATTORNEYPatented Apr. 17., 1945 APPARATUS FOR INTENSIFYING SPEECH IN 'THE HUMANVOCAL 'CAVITIES Norman E. French, Pleasantville, N. Y., assignor.

to Bell Telephone Laboratories, Incorporated, New link, N. Y., acorporation of New York Application December 11, 1943, Serial No.513,857

, 12 mm. This invention relates to a .nethod of and apparatus forenabling a speaker to deliver by his own voice speech vibration havingamplitudes whichv are larger than the amplitudes of the speechvibrations that he could produce by his vocal efiorts alone.

When a speaker is immersed in ambient noise of a high level, he usuallyfinds it diillcult to raise the level of his voice above that of thenoise near his lips, without tending to strain his voice.

This means that such unfavorable speech-tonoise ratio exists near thespeaker's lips that a listener even close to the-speaker would havedifflculty in comprehending the speech. The same diillculty would exist;when the listener moved away from the speaker; and, when the speech wasreproduced at a distance from the speaker by means of a public addresssystem or the like embodying a microphone positioned near the speaker'slips. This follows because such system a would tend to attenuate" oramplify speech and noise substantially to the same extent leavingsubstantially unchanged the speech-to-noise ratio of the transmittedspeech and noise.

The present invention is concerned with in-.

creasing the level of the speech vibrations delivered by the humanvoice, and thereby the speechto-noise ratio in proximity of thespeaker's lips.

The present invention contemplates an arrangement for mechanicallyproducing sound vibrations of certain frequencies and amplitudes andintroducing them into the vocal cavities of a speaker, together with thesound vibrations produced naturally by the speaker and thereby sub--stantially increasing the amplitudes of the speech vibrations deliveredby the voice of the speaker.

The main object of the invention i to increase the amplitudes of thefrequencies in a speech spectrum delivered by the voice of a speaker.

Another object is to increase the value of the speech-to-noise ratio ofspeech transmitted directly through an air transmission'medium whichimmerses both the speaker and listener in ambient noise. v 1

A further object is to increase the value of the speech-tomoise ratio ofspeech transmitted over a public address system arranged such that boththe speaker and microphone pick-up are immersed in ambient noise.

As a talker in noisy surroundings raises his voice to make himselfheard, he experiences difficulty because the higher voice frequencieswhich contribute greatly'to intelligibility and which are .relativelyweak may still be too close to the noise a level. evgn when the take; isshouting, Exp'efl- 5 A feature of the invention is that the mechani-"roughly the same amplitude.

The present invention aims to take advantage of this fact by providingfor selectively building up the higher frequency energy of speech wavesto enable the speech to be understood through noise In a particular casewhere the noise has a given type of frequency energy characteristic theinvention provides for predistorting the emitted voice waves to betterenable them to override the voice by givingthem an, improvedfrequency-by-irequency speech-tosnoise ratio over the band. a

In a specific embodiment, the invention comprises in sequence one ormore electroacoustic transducers applied to the skin in the region ofthe throat of a speaker, a low-pass filter, an amplifier, a harmonicproducer, a high-pass filter, a network for controlling the amplitudesof individual'frequencies, and an electrcacoustic converter whose outputis introduced into the vocal cavities of the speaker.

In operation, the sound vibrations at the surface of the skin in theregion of the throat of harmonic currents are then translated into othersound vibrations whose frequencies and amplitudes correspondsubstantially to those of the harmonic currents. These sound vibrationsare introduced into the vocal cavities of the speaker to be molded bythe cavities of his throat, mouth and nasal passages into speech,together with the sound vibrations produced naturally in the speakersthroat. Thus, the amplitudes of the speech vibrations delivered by thespeaker's voice are substantially increased with reference to the levelof the ambient noise, without requiring a noticeable increase in thevocal efforts of the speaker.

tain range of audible frequencies.

cally produced sound vibrations may be introduced into the vocalcavities of the speaker either through the mouth of the speaker, orthrough the skin in the region of the throat of the speaker. Anotherfeature concerns compensation for the vocal output of the speaker as hetends to relax his vocal efforts.

The invention will be readily understood from the following descriptiontaken together with'the accompanying drawing in which:

Fig. 1 is a schematic circuit illustrating the speciflc embodiment ofthe invention;

Fig. 2 is a family of curves illustrating action with such amplitudeversus frequency characteristic that the combined speech vibrationsdelivered by the speakers voice are provided with a favorable value ofspeech-to-noise ratio, with reference to, the ambient noise spectrum inwhich the speaker may be immersed. Compensation for .-the tendency ofthe speaker to relax his vocal eiforts is provided by the automatic gaincontrol brations'of fundamental frequency and harmonics thereof, as thespeaker produces them, and to translate such vibrations into electriccurrents of fundamental and harmonic frequencies corresponding to thoseof the sound vibrations. The microphone as shown comprises a pair ofelectroacoustic converters connected in series. In accordance with thefamiliar practice, these converters may also be connected in paralleland may comprise one or more converters as desired.

These harmonic currents are supplied to a lowpass filter H which passesthe fundamental current but suppresses the harmonicLcurrents. Thefundamental current is amplified in amplifier l2 embodying suitableautomatic gain control, and thereafter impressed on a harmonic produceri8 whose output includes both the fundamental current and harmonicsthereof extending over a cer- This range may comprise the entire audiblerange or a desired portion of it, and may correspond in toto or in partto the frequencies of the sound vibrations produced in the human throatas previously mentioned.

The harmonic currents are supplied to a highpass filter 14 which passesthe harmonic currents but suppresses the fundamental. The harmoniccurrents are then supplied to a network it which relatively varies theamplitudes of individual harmonics. For example, the range of harmoniccurrents appearing in the output of the network l5 may be preshaped withamplitudes of predetermined. relative magnitudes with reference to thespectrum of a particular ambient noise.

The latter harmonic currents are then supplied over a pair of leads l8,IE to an electroacoustic converter I1, and thereby translated into soundvibrations whose frequencies and amplitudes correspond substantially tothe frequencies and amplitudes, respectively, of the harmonic currents.These sound vibrations are introduced via a hollow tube l8 into thevocal cavities of the speaker,

such as the resonant chambers of the mouth, throat and nasal passages,for molding into audible sounds in the same manner as the molding ofnormal speech vibrations.

In the operation of Fig. l, the sound vibrations produced in thespeaker's throat are introduced into his vocal cavities for moldingintoaudible sounds which are delivered by the speaker's voice in' thefamiliar manner. The mechanically produced vibrations introduced intothe vocal cavities in the manner pointed out .above are com.-

bined with the naturally produced vibrations so of amplifier l2operating in the familiar manner. The combination of low-pass filter,harmonic producer and high-pass filter eliminates the tendency of theloop to sing. I

Fig, 2 shows the value of the speech-to-noise ratio of normal speechproduced in an assumed ambient noise spectrum; the value of thespeechto-noise ratio of the reinforced speech in the same noisespectrum; and the value of the speechto-noise ratio of the combinednormal and reinforced speech in the same noise spectrum. From Fig. 2, itis readily apparent that the amplitudes of the speech vibrationsdelivered by the speaker's voice, in accordance with the presentinvention, are substantially increased with reference to the amplitudesof the normal speech, and with reference to amplitudes of the noise inthe assumed ambient noise spectrum in which the speaker is immersed. Inthe latter connection it is apparent that amplitudes of the combinedmechanical and natural speech vibrations of the speaker aresubstantially increased without affecting either his vocal efforts orthe level of the ambient noise. It will be noted that the summationcurve representing normal speech plus reinforced speech indicates a lessfavorable addition than arithmetic addition to take account of possibleout-of-phase relation that may be present.

Referring to Fig. 1, the speaker may apply the speech delivered by hisvoice to a microphone 20 connected by a pair of leads 2i, 2! toasuitable public address system or the like, not shown, where both thespeaker and microphone 20 are immersed in an ambient noise spectrum of.a high level. When the listener, at the remote end of the public addresssystem, is immersed in ambient noise which has a level equal to or lessthan that in proximity of the speaker, such listener would obtainsubstantially the full benefit of the improved speech-to-nolse ratioproduced at the microphone in accordance with the present invention ashereinbefore described.

a noise which has a level higher than that in proxi- A obtain benefitfrom the improved speech-to noise,

mity of the microphone, such listener would also ratio at the microphonein a manner that will now be explained. This is. accomplished byincreasing the gain of the public address system to such value that thetransmitted noise is reproduced at the listening location at a level.which is higher than that of the noise at the listening location. Thismeans that, at the same time, the transmitted speech is also reproducedat the listening location at an increased level which maintains thespeech-to-nolse ratio produced at the microphone as above mentioned.Should the transmitted speech be reproduced at a level too high forphysical comfort, the listener may restore the reproduced speech to acomfortable level by employing ear defenders, or similar means, forattenuating both the speech and noise-in the ear canal before they reachthe ear drum.

Referring to Figs. 1 and 3, the sound vibrations produced in accordancewith Fig. i may be applied directly to the skin in the, region ,of thethroat of the speaker as shown in Fig. 3, and thereby introduced' intothe vocal cavities of the speaker. In this connection, it is understoodthe circuit portion shown to the left of the line XX in Fig 3 may besubstituted for the circuit shown to the left of the line X-X in Fig. 1;and further the operation of Figs. 1 and 3 is substantially the same asthat hereinbefore explained with reference to Fig. 1.

In Fig. 4 the harmonic currents supplied over the pair of leads I6, l6are divided into three bands by the band-pass filters 25, 26 and 21, and

thereafter into three bands of corresponding sound vibrations by theelectroacoustic converters 29, 30 and 3|, respectively. This serves toreduce the peak factors which tend to increase the required maximumexcursion of'the diaphragm of the electroacoustic converter l7, Fig. 1.

In Figs. 1, 3 and 4, the microphone and associated public address systemmay be omitted so that the speech is directly transmitted through theair as the transmission medium from the speaker to the listener, whereboth the speaker and listener may be immersed in an ambient noisespectrum as 'hereinbefore mentioned. The arrangements'of Figs. 1, 3 and4 minus the public address system operate substantially identically asdescribed previously in connection with Figs. 1, 3 and 4 using thepublic address system.

What is claimed is:

1. In reinforcing'the amplitudes of speech vibrations produced in thevocal organism of a human and delivered by the human voice, includingsound vibrations of fundamental and harmonic frequencies in the regionof the skin of the v human throat after being naturally producedtherein, the-methodwhich comprises translating the fundamental soundvibration picked up from the skin of the throat into a plurality ofother sound vibrations extending over a certain audible frequency rangecorresponding at least in part to the frequency range ofthe vibrationsproduced in the throat but not including the fundamental vibration, andhaving amplitudes increasing with frequency over said part of saidcertain frequency range, and introducing 'said other sound vibrationsinto the vocal cavities of the human for molding into articulate sounds,together with the vibrations naturally produced in the human throat,whereby the amplitudes of the speech vibrations delivered by the humanvoice are substantially reinforced.

2. In reinforcing the amplitudes of speechvibrations produced in thevocal organism of a human .and delivered by' the human voice, in-

cluding sound vibrations of fundamental and ban monic frequencies in theregion of the skin of the human throat after being naturally producedtherein, the method which comprises translating said fundamentalvibration picked up from the skin of the throat into a plurality ofelectrical currents havingfrequencies related harmonically to saidfundamental vibration and extending over a certain range of audiblefrequencies, translating said harmonic currents. into "a plurality ofsound vibrations whose energy is lower than normay speech energy at oneend of the speech range but higher than normal speech energy at the 7its amplitude to opposite end of the speech range, and introducing thelatter sound vibrations into the human vocal cavities for molding intoaudible sounds, together with the vibrations naturally produced in thehuman throat, thereby substantially increasing the amplitudes of thespeech vibrations delivered by the human voice.

3. The method of increasing the amplitudesof speech vibrations producedin the vocal organs of a human and delivered by the human voice,including sound vibrations of fundamental and harmonic frequencies atthe skin in the vicinity of the human throat after being naturallyproduced therein, which method comprises picking up the sound vibrationsfrom the human throat and translating them into an electric current of afundamental frequencyv corresponding to that of said sound vibrations,translating said fundamental current into a plurality of harmoniccurrents whose frequencies extend over a certain audible frequency rangecorresponding at least in part to the frequency range of the vibrationsproduced in the throat but not including current of the fundamentalfrequency, preshaping the amplitudes of, said harmonic currents,converting the preshaped harmonic currents into sound vibrations, andintroducing the latter sound vibrations into the vocal cavities of thehuman for molding into articulate sound, together with thespeechvibrations naturally produced in the human throat, therebysubstantially increasing the amplitudes of the speech vibra tionsdelivered by the human voice.

4. In speech transmission in ,noisy surroundings the method comprisingpicking up vocal energy from the talker with a high speech-tonoise.ratio compared with the ratio existing in noise of a predominantfrequency characteristic,

the method comprising picking up vocal energy directly from the talkersvocal parts at a point where the speech-to-noise ratio is higher than inthe surrounding up energy a sound wave in which'the ratio of highfrequency level to .low frequency level is .much greater than in thecase of normal speech, shaping said sound wave with respect to the noisefrequency characteristic to increase the ratio of that of the noise,frequency for frequency, and introducing said shaped sound wave into thetalkers vocal cavities to be molded by the talker's vocal parts intoarticulate speech.

6. In combination in apparatus for increasing.

the amplitudes of speech vibrations in the vocal organism ofa speakerand delivered by his voice, means for picking up the fundamentalvibration from the speaker and translating it into a plu-" rality ofsound vibrations having frequencies extending over all but the lowerportion of the speech range and having amplitudes preshaped such thatthose or the higher frequencies are larger than-those of the lowerfrequencies and means for introducing the latter sound vibrations intothe human vocal cavities for molding into portion of the band, relativeto air, deriving from such picked- I articulate sound, together withvibrations produced. in the throat, whereby the amplitudes of the speechvibrations delivered by the human voice are substantially increased.

7. In combination-in apparatus for increasing the amplitudes of speechvibrations produced in the vocal organism of a talker immersed in anambient noise spectrum and delivered ,by his voice-means for picking upvocal energy from they talker and translating it into a plurality ofharmonic'currents, and means for translatin said harmonic currents intosound vibrations and for introducing the latter sound vibrations intothe vocal cavities of the talker for molding into articulate sounds,together with the sound vibrations naturally producer-lv in his throat,so that the amplitudes of the speech vibrations emitted from the talkerslips are substantially increased with reference to the amplitudes of thefrequencies in the ambient noise spectrum.

8. The combination according to claim 7 in I which said fundamentaltranslating means inchides means for relatively varying the amplitudesof individual harmonic currents.

9. The combination according to claim '7 in which said harmonic currenttranslating means comprises means for introducing the latter soundfundamental current to produce harmonic currents whose frequenciescorrespond at leastin produced in the throat, so as to reinforce theamplitudes of the speech vibrations delivered bythe human voice. i V

12. A system for'reinforcing the intensity of speech produced in thevocal organism of a vibrations into the vocal cavities of the talkerthrough his mouth. a

10. The combination according to claim 7 in which said harmonic currenttranslating means comprises means for introducing the latter soundvibrations into the vocal cavities of the talker through-the skin in theregion of his throat;

11. In combination in apparatus for reinforcing the amplitudes of speechvibrations produced in a the vocal organism of a talker and delivered byhis voice, including sound vibrations of fundamental and harmonicfrequencies in the region of the skin of the talkers throat after beingnaturally produced therein, means for picking up the vibrations from theskin of the throat and speaker immersed inambient noise and delivered byhis voice, comprising in sequence, means ap-, plied to the surface ofthe skin of the speaker's throat for picking up sound vibrations offundamental and harmonic frequencies and translating them into speechcurrents including a current of fundamental frequency and currentsharmonlcally related to said fundamental frequency,

means for selecting said fundamental current 1 and suppressing saidharmonics thereof, means for amplifying said fundamental current, meansfor utilizing said amplified fundamental current to produce furtherharmonic currents, means for selecting said further harmonic currentsand suppressing said fundamental current, means for relatively varyingthe amplitudes of individual further harmonic currents, and means fortranslating the varied harmonic currents into sound vibrations, and forintroducing the latter sound vibrations into the vocal cavities of thespeaker for molding intoarticulate sounds, together with the vibrationsnaturally produced in the speaker's translating them into an electriccurrent of a fundamental frequency, means for utilizing said throat, andtherebysubstantially reinforcing the amplitudes of the speech vibrationsdelivered by the human voice, with reference to the ambient noisespectrum. s 1

NORMAN R. FRENCH.

